Technical Field
The technical field relates generally to state control of electrical systems on motor vehicles, and more particularly to state control over power distribution systems for hybrid vehicles equipped with electric traction motors and internal combustion engines.
Description of the Technical Field
A familiar feature of motor vehicles equipped with internal combustion engines has been the rotary, four position ignition switch. The usual positions and arrangement provided by these ignition switches include, advancing in a clockwise direction, an ACCESSORY position, an OFF position, an ON position and a START position. Prior to the introduction of computer systems for control of motor vehicles, ignition switches were electro-mechanical devices where each position corresponded directly to a particular state of the electrical system on the vehicle, provided the vehicle battery was not dead. With the switch in the “accessory” position vehicle systems such as the engine ignition system (on spark ignition engines) were cut off from power but a limited set of electrical components, such as a radio, were allowed to draw power from the vehicle battery. The off position of the ignition switch was the most restrictive state with only a very few components, such as a vehicle clock, which had a direct connection to the vehicle battery able to receive power. In the run or ON position of the rotary ignition switch the engine was usually running, but whether running or not virtually all electrical systems were allowed to draw power excluding the cranking motor. In the start position the starter motor and any electronics used to crank and start an internal combustion engine were operative while other electrical components were temporarily disabled to increase available power.
Motor vehicles have seen the increasing use of computer control over vehicle operation. Hybrid-electric vehicles are increasingly common, particularly for commuter vehicles and urban delivery applications. Notwithstanding these developments many familiar control elements are often retained, such as a control element emulating the four position ignition switch. Emulation of familiar control elements provides an intuitive feel to vehicles and can simplify a driver's transition to such vehicles. Body computers (and analogous systems), on board networks and hybrid-electric vehicles have made the relationship between ignition switch position and the vehicle electrical system state an indirect one. The indirectness of the relationship stems in part from the fact that the “ignition switch” control element no longer provides a direct mechanical link to a power circuit breaker for most vehicle systems. The contemporary ignition switch operates as a data input source for the vehicle body computer which in turns controls relay and switch states. In addition, hybrid-electric vehicles are more likely to have distinct power distribution sub-systems operating at different voltages. As a result there are a greater number of potential electrical system states than the four found on most 20th century internal combustion engine vehicles.
The possibility of a large number of electrical states is common to hybrid-electric vehicles, which can have different power distribution sub-systems operating at different nominal voltage levels and may include direct current (DC) or alternating current (AC) sub-systems. The differentiation between power distribution sub-systems and the increasing number of electrified accessories, such as electrical motors for power steering, increases the number of possible energization states that the overall power distribution system can assume. The presence of multiple voltage levels on the vehicle and the high current levels possible on some of these system compared to prior 12-volt DC electrical systems can complicate transitions between states of the electrical system.
A traditional rotary ignition switch provided a hardwired, manually operated switch for isolating much of the electrical distribution system of a vehicle from the vehicle's battery. Contemporary electronic controls use an “ignition switch” as a data source. Because of this it is not a manual fail safe to isolate the power distribution system from electrical power source. Because of this electric and hybrid-electric vehicles are usually configured with one or more hardwired switches independent of the computerized control system which can be used in an emergency for isolating the vehicle's electrical prime movers or accessory sub-systems from the source of electrical power and for preventing these sub-systems from reinitializing. These switches may be automatic, manual or both, but in any event they operate independently of the electronic control system to allow a forced shut down of the high voltage sub-systems on a vehicle. In hybrid-electric vehicles such forced shutdowns can produce abrupt power interruptions which can result in damage to the high voltage contactors and other components, particularly when substantial amounts of current are flowing through the contactors, because power interruption can take place outside of a normal computer implemented power shut down protocol and occur without prior load shedding.